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Refmap warnings are cluttering the log

Q: What does "Reference map 'sodium-refmap.json' for sodium.mixins.json could not be read. If this is a development environment you can ignore this message" mean?

Refmap warnings are cluttering the log. A "reference map could not be read" warning on its own is usually harmless build noise from a mod, not the cause of a crash. Ignore these lines unless a real mixin failure appears further down. They only matter when paired with an injection error.

Q: How do I fix "Reference map 'sodium-refmap.json' for sodium.mixins.json could not be read. If this is a development environment you can ignore this message"?

1. Read past it: Scroll down from the warning. If the server reaches "Done" or the world loads, nothing is wrong. 2. Look for a real injection failure: A MixinApplyError, "Critical injection failure" or an AbstractMethodError further down is the actual fault. The refmap warning may sit next to it, but the failure line names the mod. 3. Stop pasting it as the error: When asking for help, paste the crash report or the lines after the last start-up line. The refmap warnings are the first thing people see and the last thing that matters.

Applies to Forge, NeoForge, Fabric, Quilt.

What it looks like in your log

Reference map 'sodium-refmap.json' for sodium.mixins.json could not be read. If this is a development environment you can ignore this message

What causes it

A "reference map could not be read" warning on its own is usually harmless build noise from a mod, not the cause of a crash.

How to fix it

Ignore these lines unless a real mixin failure appears further down. They only matter when paired with an injection error.

Why it happens

A reference map is a file inside a mod that translates the readable names its mixins were written against into the obfuscated names the game uses at runtime. When the mod was built without one, or the loader already runs with readable names, the warning appears once per mixin config at start-up.

It is a message meant for mod developers running a development environment. On a server it is ignorable, and the line itself says so. It tells you nothing about why a server crashed, and it appears in perfectly healthy logs.

Fix it step by step

1Read past itScroll down from the warning. If the server reaches "Done" or the world loads, nothing is wrong.
2Look for a real injection failureA MixinApplyError, "Critical injection failure" or an AbstractMethodError further down is the actual fault. The refmap warning may sit next to it, but the failure line names the mod.
3Stop pasting it as the errorWhen asking for help, paste the crash report or the lines after the last start-up line. The refmap warnings are the first thing people see and the last thing that matters.

If that didn't work

If a helper insists this line is the cause, ask them for the injection failure it supposedly led to. There will not be one.

Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.

Check your own log